Cesanta Mongoose before 7.22 contains an out-of-bounds read in the built-in TLS server function mgtlsserverrecvhello(), which uses an attacker-controlled sessionidlen byte from a TLS ClientHello as a buffer index without validating it against the length of received data. A remote, unauthenticated attacker can send a single crafted ClientHello with an oversized session id length to read past the receive buffer, crashing any HTTPS, MQTTS, or WSS service built on MGTLSBUILTIN.

Mongoose is an embedded web server and network library. Prior to 7.22, a remote unauthenticated attacker can exploit an HTTP/1.0 reverse-proxy deployment by sending a request with Transfer-Encoding: chunked and conflicting framing. The httpcb() function in src/http.c tests hm.proto.len with an impossible greater-than-eight condition even though mghttpparse() requires an eight-byte protocol string, so ishttp10 is never set. Mongoose consequently processes chunked encoding that an HTTP/1.0 proxy can ignore, enabling request smuggling and unauthorized access or state changes. This issue is fixed in version 7.22.

A weakness has been identified in Cesanta Mongoose up to 7.20. This vulnerability affects the function handleopt of the file /src/netbuiltin.c of the component TCP Option Handler. This manipulation of the argument optlen causes infinite loop. The attack is possible to be carried out remotely. The exploit has been made available to the public and could be used for attacks. Upgrading to version 7.21 is able to resolve this issue. Upgrading the affected component is advised. VulDB has contacted the vendor early and they confirmed quickly, that this issue got fixed already.

A security vulnerability has been detected in Cesanta Mongoose up to 7.20. This issue affects the function mgaesgcmdecrypt of the file /src/tlsaes128.c of the component GCM Authentication Tag Handler. Such manipulation leads to improper verification of cryptographic signature. The attack may be performed from remote. A high complexity level is associated with this attack. The exploitability is assessed as difficult. The exploit has been disclosed publicly and may be used. Upgrading to version 7.21 is capable of addressing this issue. It is advisable to upgrade the affected component. VulDB has contacted the vendor early and they confirmed quickly, that this issue got fixed already.

The HTTP server in Mongoose before 7.10 accepts requests containing negative Content-Length headers. By sending a single attack payload over TCP, an attacker can cause an infinite loop in which the server continuously reparses that payload, and does not respond to any other requests.

Use-after-free vulnerability in the mghttpmultipartwaitforboundary function in mongoose.c in Cesanta Mongoose Embedded Web Server Library 6.7 and earlier and Mongoose OS 1.2 and earlier allows remote attackers to cause a denial of service (crash) via a multipart/form-data POST request without a MIME boundary string.

A vulnerability has been found in Cesanta Mongoose up to 7.20. This affects the function mgtlsrecvcert of the file mongoose.c of the component TLS 1.3 Handler. Such manipulation of the argument pubkey leads to heap-based buffer overflow. The attack may be launched remotely. The exploit has been disclosed to the public and may be used. Upgrading to version 7.21 mitigates this issue. The name of the patch is 0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1. It is advisable to upgrade the affected component. The vendor was contacted early, responded in a very professional manner and quickly released a fixed version of the affected product.

A vulnerability was found in Cesanta Mongoose up to 7.20. This impacts the function handlemdnsrecord of the file mongoose.c of the component mDNS Record Handler. Performing a manipulation of the argument buf results in stack-based buffer overflow. Remote exploitation of the attack is possible. A high degree of complexity is needed for the attack. The exploitability is said to be difficult. The exploit has been made public and could be used. Upgrading to version 7.21 will fix this issue. The patch is named 0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1. You should upgrade the affected component. The vendor was contacted early, responded in a very professional manner and quickly released a fixed version of the affected product.

A vulnerability was determined in Cesanta Mongoose up to 7.20. Affected is the function mgtlsverifycertsignature of the file mongoose.c of the component P-384 Public Key Handler. Executing a manipulation can lead to authorization bypass. The attack can be executed remotely. Attacks of this nature are highly complex. The exploitability is told to be difficult. The exploit has been publicly disclosed and may be utilized. Upgrading to version 7.21 is able to address this issue. This patch is called 0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1. The affected component should be upgraded. The vendor was contacted early, responded in a very professional manner and quickly released a fixed version of the affected product.

Cesanta Mongoose commit b316989 was discovered to contain a NULL pointer dereference via the scpy function at src/fmt.c. This vulnerability allows attackers to cause a Denial of Service (DoS) via a crafted MQTT packet.

Mongoose network library <= 7.20 CVE-2026-5244 - mg\tls\recv\cert pubkey heap-based overflow (exploitable) CVE-2026-5245 - mDNS Record stack-based overflow (exploitable) CVE-2026-5246 - authorization bypass via P-384 Public Key (trivially exploitable)

Fun ride.

A weakness has been identified in Cesanta Mongoose up to 7.20. The impacted element is the function mgsendnsreq of the file /src/dns.c of the component DNS Transaction ID Handler. Executing a manipulation of the argument random can lead to insufficiently random values. The attack can be launched remotely. The attack requires a high level of complexity. The exploitability is regarded as difficult. The exploit has been made available to the public and could be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way.

A security vulnerability has been detected in Cesanta Mongoose up to 7.20. This affects the function getpeer of the file /src/netbuiltin.c of the component TCP Sequence Number Handler. The manipulation leads to improper verification of source of a communication channel. The attack may be initiated remotely. The attack's complexity is rated as high. The exploitability is reported as difficult. The exploit has been disclosed publicly and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

A vulnerability was detected in Cesanta Mongoose up to 7.20. This impacts the function mgchacha20poly1305decrypt of the file /src/tlschacha20.c of the component Poly1305 Authentication Tag Handler. The manipulation results in improper verification of cryptographic signature. The attack may be launched remotely. This attack is characterized by high complexity. The exploitability is said to be difficult. The exploit is now public and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

Null pointer dereference in addcacerts() in Cesanta Mongoose before 7.2 allows remote attackers to cause a denial of service via TLS initialization where SSLCTXgetcertstore() returns NULL.

Integer Overflow or Wraparound vulnerability in Cesanta Mongoose Web Server v7.14 allows an attacker to send an unexpected TLS packet and produce a segmentation fault on the application.

An integer overflow vulnerability exists in the WebSocket component of Mongoose 7.5 thru 7.17. By sending a specially crafted WebSocket request, an attacker can cause the application to crash. If downstream vendors integrate this component improperly, the issue may lead to a buffer overflow.

An issue in Cesanta mjs 2.20.0 allows a remote attacker to cause a denial of service via the mjsgetretvalpos function in the msj.c file.

An issue in Cesanta mjs 2.20.0 allows a remote attacker to cause a denial of service via the mjsdestroy function in the msj.c file.

An issue in Cesanta mjs 2.20.0 allows a remote attacker to cause a denial of service via the mjs+0x4ec508 component.

An issue in Cesanta mjs 2.20.0 allows a remote attacker to cause a denial of service via the mjsarraylength function in the mjs.c file.

An issue in Cesanta mjs 2.20.0 allows a remote attacker to cause a denial of service via the mjsmkffisig function in the mjs.c file.

An issue in Cesanta mjs 2.20.0 allows a remote attacker to cause a denial of service via the mjsdogc function in the mjs.c file.

An Out of Bounds Write in Cesanta mjs 2.20.0 allows a remote attacker to cause a denial of service via the mjsopjsonstringify function in the msj.c file.

Cesanta Software Mongoose-OS v2.17.0 is vulnerable to integer wrap-around in function mmmalloc. This improper memory assignment can lead to arbitrary memory allocation, resulting in unexpected behavior such as a crash or a remote code injection/execution.

Buffer Overflow vulnerability in Cesanta mJS 1.26 allows remote attackers to cause a denial of service via crafted .js file to mjsseterrorf.

An Allocation of Resources Without Limits or Throttling vulnerability in Cesanta Frozen versions less than 1.7 allows an attacker to induce a crash of the component embedding the library by supplying a maliciously crafted JSON as input.

A NULL Pointer Dereference vulnerability in Cesanta Frozen versions less than 1.7 allows an attacker to induce a crash of the component embedding the library by supplying a maliciously crafted JSON as input.

Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via gcsweep at src/mjsgc.c. This vulnerability can lead to a Denial of Service (DoS).

Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via fficbimplwpwwwww at src/mjsffi.c. This vulnerability can lead to a Denial of Service (DoS).